And then his commander said : " Levi , there is a titan at ( whatever place ) . It dirtied your office and bedroom just now . Then Levi growled : " Oh , really? Then I know what it 'a name is , Hanji . " ( runs off to punish her . )

He's putting his own fingers on the screen as he cleans. And if he swaps hands, he'll end up putting his fingers where he just cleaned. No matter how clean his hands are, they will smudge the screen. He'll get to clean forever!